The problem is caused by the pitch fader range being set to zero on fresh builds. I made a pull request on GitHub: https://github.com/mixxxdj/mixxx/pull/1206 catching pitch fader ranges <= 0.0
After starting Mixxx a second time (after a graceful shutdown), the pitch range value gets read from the ~/.mixxx/mixxx.cfg and the problem doesn't occur any more. Details in the PR.